1. Field of the Invention
The present invention is directed to netless fiber mulch mats, to a process for their preparation, and to their use.
2. Background Art
Fiber mulch mats are in widespread use in preventing soil erosion and to aid in germination of seed beds. The fibers in such mats, also termed turf reinforcement mats (“TRM”) may be derived from numerous organic sources, including wood fibers, straw, jute, sisal, coconut, and paper. Due to its ready availability, wood fibers are preferred for such products.
Fiber mulch mats must possess satisfactory physical characteristics which are often conflicting. For example, the mats should aid in water retention when used to aid seed germination, yet must be open enough to allow seedlings to penetrate the mat. The mats must also be of sufficient strength to be handled effectively during installation over soil and/or seedbeds, and must retain their integrity over extended periods while exposed to the elements. Otherwise, their ability to control run-off, and hence erosion, would be rapidly lost.
In the past, fiber mats have been bound together with the aid of numerous organic binders, both natural and synthetic. Natural binders include starches, vegetable gums, and the like, including chemically modified celluloses such as hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and the like. Such natural or chemically modified natural binders suffer from the defect of rapid degradation due to exposure and to the action of microorganisms. Synthetic polymeric binders such as styrene-butadiene latexes, polyacrylates, polyacrylamides, acrylic acid/acrylamide copolymers, polyvinylacetate, polyvinylacetate-ethylene copolymers, phenolic resins, and the like have also been used. Such polymer-based binders are generally more expensive than natural binders, and many share at least modest water solubility or swellability, which decreases the binding capability and hence strength of the product over time following installation. Even directly after manufacture, such products frequently exhibit deficient strength properties.
In U.S. Pat. No. 5,779,782, binding of spray-applied fiber mulch mats is improved by the incorporation of crimped synthetic fibers which serve to entangle with other crimped synthetic fibers and natural fibers to increase the integrity of spray applied mats while employing less or no binder. In U.S. Pat. No. 6,360,478, it is proposed to employ permanently crimped natural fibers for a similar purpose. No preformed mats are disclosed, however, and the degree of entanglement of either natural or synthetic fibers, without the use of a binder, is not believed possible to formulate a mat with adequate tear strength or tensile strength.
In U.S. Pat. Nos. 5,779,782, 5,330,828 and 5,484,501, it is proposed to employ low melting organic polymer fibers together with natural mulch fibers. The mat is preferably air laid, and passes through a heated embossing roller which melts portions of the organic fibers, thus binding together the mulch fibers. However, in this process, the strength-imparting properties of the polymer fibers is substantially lost, and the addition of further high melting fibers is suggested to overcome this deficit. Such mats also possess less than the desired degree of tensile strength and tear resistance.
All the foregoing mat products suffer from a lack of tensile and tear strength, and thus it has been proposed to further incorporate fiber netting to increase these characteristics, as taught, for example by U.S. Pat. No. 5,302,445. The netting is preferably of low melt temperature polypropylene, and is sandwiched between two fibrous mulch mats. Upon being calendared between heated rollers, the net serves both as a binding aid as well as a reinforcing aid. However, the primary binding of the mulch fibers is accomplished with the aid of conventional natural or synthetic binders such as starch or phenolic resin. A typical binder-bound, polymer net-containing product of the prior art is illustrated in FIG. 1, where the wood fibers 2 of the mulch mat 1 are intertwined and bound by a binder which is not apparent in this view since it generally is applied as a solution or a dispersion of very fine particles in the nature of wood glue, and binds the wood fibers 2 where they touch each other. The polymer netting 3 further secures the wood fibers and renders the mat tear resistant.
Mats containing polymer netting are sometimes undesirable. First, portions of the netting, due to exposure, particularly to UV light, may lose their strength rapidly, while other portions which become encased in soil and sediment may persist for many years, resulting in an environmentally undesirable contaminant. Such netting is also susceptible to entanglement by animal traffic, which may result in tearing or displacement of the mat, or the ensnaring of small animals, and to damage by equipment such as lawn mowers and the like. Commercial products may also exhibit less than adequate water holding capacity, as well as lesser ability to conform to the terrain due to the increase in stiffness provided by the netting. Close contact with ground contours is desirable to reduce run-off and soil erosion.
It would be desirable to provide a mulch mat consisting largely of natural fibers which possesses adequate strength properties without the use of netting, the properties of which are enduring even when exposed to the elements and microorganisms. Such a product should be economical to manufacture, and should possess the characteristics desirable for seed bed establishment and/or erosion control. It would be further desirable to produce such a mulch mat with no or little natural or synthetic binder.